(1) Field of the Invention:
The present invention relates to a rubber composition for tires which contains novel polybutadiene.
(2) Related Art Statement:
Heretofore, in order to maintain abrasion resistance, high cis 1,4-polybutadiene as well as natural rubber, high cis 1,4-polyisoprene and styrenebutadiene copolymer have been used in rubber compositions for tire treads. However, rubber compositions containing high cis 1,4-polybutadiene are inferior in that dispersing speed of carbon black as a reinforcing material is slow and its dispersibility is poor during kneading by a Banbury mixer, a plast mill or the like. If the dispersibility of carbon black into a rubber composition is attempted to be improved, there occurs problems that the rubber composition is liable to burn or gelate. If the dispersibility of carbon black is poor, there occur various problems that extrusion skin is bad when a kneaded composition is extruded, dimensional stability in the extrusion is poor, and an extruding speed is low.
On the other hand, if rubber compositions containing low cis 1,4-polybutadiene containing 10 to 30% of bound vinyl groups is used instead of high cis 1,4-polybutadiene, there are problems in terms of physical properties of vulcanizates that abrasion resistance and breaking strength are poor, although the problems during kneading are lessened.